The Formation of N<sub>2</sub>O on the SCR Catalyst in a Heavy Duty US 2010 Emission Control System

Kevin Hallstrom; Kenneth E. Voss; Sandip Shah

doi:10.4271/2013-01-2463

A heavy duty US 2010/Euro VI type emission control system typically consists of diesel oxidation catalyst (DOC), catalyzed soot filter (CSF), urea based selective catalytic NOx reduction (SCR) and NH₃ slip control catalyst (AMOX - excluded for this study). The advent of the US 2014 Green House Gas (GHG) rules has established a limit for tailpipe N₂O emissions for on-road heavy duty Diesel engines, thus creating new challenges for catalyst design and system/engine calibration.

In this paper, we discuss the effects of both catalyst system design and engine calibration on the formation of N₂O across SCR catalysts. This study consisted of system testing on engine, modeling and component reactor testing. These three tools were used to evaluate how NO₂ to NO_x ratio and ammonia to NO_x ratio (ANR) affect N₂O formation.

The study showed that all of the reviewed factors affect tailpipe N₂O emissions. The amount of NO₂ entering the SCR showed the greatest affect, particularly when the NO₂ to NO_x ratio is greater than 50%. Increasing the ANR also increased the N₂O but to a lesser degree than the NO₂/NO_x ratio. The effect that the ANR had on N₂O was also dependent on the temperature of the test cycle which is confirmed by reactor data showing the optimal temperature for forming N₂O peaked at approximately 250°C.

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The Formation of N ₂ O on the SCR Catalyst in a Heavy Duty US 2010 Emission Control System 2013-01-2463

SAE MOBILUS

The Formation of N 2 O on the SCR Catalyst in a Heavy Duty US 2010 Emission Control System 2013-01-2463

SAE MOBILUS

The Formation of N ₂ O on the SCR Catalyst in a Heavy Duty US 2010 Emission Control System 2013-01-2463